"Bikepacking" is really just a fancy word for bicycle touring. If you're on a modern hardtail, you're probably not going to be using panniers, so you want a seatbag in the style of the Revelate, of which there are now about a zillion knockoffs. On the front, you will probably add a "roll" bag, meaning a long tube-shaped bag with Velcro straps that go around the handlebar. Next you have the frame bag, which can be really useful, but can also severely limit the amount of water you can carry, depending on the size. You can get frame bags made for specific frames, which fit perfectly, or you can buy a generic frame bag which will usually attach to the toptube and leave your bottle unmolested. Finally, I recommend a stem bag or two like the kind Revelate created, for which there are again myriad cheap knockoffs that work just fine.
If you end up using a full-size frame bag, you can carry your water by attaching something
like this to another part of the frame or your fork, and attaching water bottles there.
All of these bags are expensive if you're buying Swift, RandiJo, Revelate, Ron's, etc. But honestly, you could probably outfit yourself with an entire "bikepacking" kit like this for under $200 buying the generic bags on eBay/Amazon.
Or, do what I do and ride an old mountain bike with panniers.